As an example of a method of obtaining a laser beam of a deficient wavelength that cannot directly oscillate the laser beam from a gas-state laser, a laser diode (LD), and a solid-state laser, one method has been suggested in Non-Patent Document 1 to be described below. According to this method, oscillation light (having a wavelength of 1122 nm) from an LD pumped solid-state laser is caused to be incident on a second harmonic generating element as fundamental light so as to be subjected to a wavelength conversion, thereby obtaining a laser beam having a wavelength of 561 nm.
Further, a method has been known which obtains a laser beam whose wavelength is converted by sum frequency generation using two laser beams having different wavelengths (for example, Non-Patent Document 2).
(Non-Patent Document 1) OSA TOP Vol. 10 “Advanced Solid State Lasers, 1997, p. 77, A Diode Pumped Solid State Yellow Laser at 564. 5 nm”, by X. X. Zhang and W. L Zhou.
(Non-Patent Document 2) “keyword explanation, optical technology general dictionary” published by OPTTRONICS on Dec. 12, 2004, p. 442
However, according to the method disclosed in Non-Patent Document 1, since a structure of the apparatus becomes complicated and a laser host material is high-priced, the cost of the laser is increased. Accordingly, the method is not practical.
According to the method disclosed in Non-Patent Document 2, since two laser light sources are used, the cost of a laser is increased, and a structure of a driving power supply of an optical source becomes complicated. Therefore, this method is also not practical.
The invention has been made to solve the above-described problems, and it is an object of the invention to provide an apparatus and a method of generating a laser beam in which a structure of the apparatus is simple, the laser beam having a predetermined wavelength can be stably generated, and practicability is excellent with the low cost.